1. Field of the Invention
The present invention relates to the testing of liquid crystal displays and more particularly concerns improved methods and apparatus using flexible circuits with bumps for testing purposes.
2. Description of Related Art
Liquid crystal display devices are being produced in ever increasing numbers, particularly as popularity of the portable lap-top type computer is rapidly growing. The screen of many lap-top computers is a flat liquid crystal display device formed by a device panel having as many as two to five thousand electrically conductive circuit lines extending to the edges of its four sides for connection to input/output display circuitry. A thin flat member overlies the panel and the circuit lines and has outer edges that run parallel to the rows of contacts formed by the ends of the conductive circuit lines. The edges of the overlying thin flat member are positioned closely adjacent the ends of the display device contacts that are defined by the ends of the lines.
As with all electronic device system components, it is desirable to test operability of the liquid crystal display devices before assembly of the computer and before assembly of the display device with its input/output circuitry. Conventional testing employs test cards provided with a number of small blades or needles often formed of a resilient or spring-like tungsten. The blades or needles are mechanically and electrically connected to a test circuit board and act as contacts with the display device to be tested. The needles are mounted with configuration and spacing to enable each needle to individually contact one and only one circuit line of the device under test. Electrical leads extend from the contacts to the outer edge of the board for connecting the probe card to test circuitry. In use the test board with its needles is moved into engagement with ends of lines on the liquid crystal display device. For proper positioning the individual blades or needles must be individually adjusted. This adjustment is accomplished by bending the resilient needles to produce a pattern and spacing to match the existing pattern and spacing of the lead ends of the display device which is to be tested.
Ends of the needles and blades must all fall in the same plane in order to assure that each one makes electrical contact with a conductive trace on the device under test. This is accomplished by bending the blades after they are mounted on the probe card, which is laborious, time consuming and expensive. Even after such adjustment the needles tend to creep back toward their original position so that their adjusted locations are lost. This loss of adjustment also comes about from the pressure of the needles against the device to be tested, aggravated by scrubbing action, where such is necessary or desired to assure penetration of an oxide that may cover circuit lines. As a result, constant maintenance is necessary or the probe cards will not perform their intended function. Even when in proper adjustment the needles cannot compensate for significant differences in planarity of the liquid crystal faces or the conductive line ends, and thus some needles may apply excessive force against the display device, thereby damaging some of the leads. Furthermore, close spacing necessary for testing exceedingly fine pitch lines (0.004 to 0.005 inch pitch for example) cannot be achieved with conventional needle contacts, or, at best, makes the test probes very expensive and susceptible to mechanical damage during testing.
Further, in test of a liquid crystal display panel, the close proximity of the edge of the overlying member to the ends of the conductive lines on the display device define a very small clearance, thus requiring ever more accurate and precise positioning of the needle contacts in order to avoid interference with the edge of the overlying member.
Accordingly, it is an object of the present invention to provide for testing by methods and apparatus that avoid or minimize above mentioned problems.